Abstract A system and structure is shown for detecting and responding to differences in potential which may exist between a reference potential which will be referred to herein as reference ground and one or more of a plurality of other metallic objects. A pair of grounding conductors is used for each object and an indication is obtained if the difference of potential between the end point of the two grounding conductors connected to the chassis of the associated object, and the reference ground, exceeds a predetermined value. An indication is also provided if the loop formed by the two grounding conductors and the chassis exceed a predetermined resistance value. The indication of the difference of potential is an indication of the potential difference between the various metallic objects, or chassis, in the system. The measurement of the loop resistance value is a measurement of the ground wire integrity and assures that the requisite low resistance exists for accurate potential difference measurements. Working in combination the measurement provides an indication of whether or not the environment is an equipotential environment and/or the difference in potential between any particular object and the reference ground.
A circuit for monitoring a chassis relative to a reference potential comprising in combination; a. a reference potential; b. a chassis; c. a first conductor having distributed resistance coupling said reference potential and said chassis for conducting current in response to a potential difference between said chassis and said reference potential; d. a series circuit comprising a second conductor having a distributed resistance comparable to that of said first conductor and an impedance having a resistance at least a few times greater than that of said distributed resistance and with said series circuit in parallel with said first conductor for conducting current in response to a potential difference between said chassis and said reference potential; e. first and second frequency sensitive potential detecting means in parallel with said impedance for monitoring the potential across said impedance, said last named potential being a function of the potential between said chassis and said reference potential; and f. a power source in parallel with said impedance and having a predetermined frequency, which differs from that of any power supply coupled to any apparatus contained within said chassis, for providing current to said first conductor and said series circuit, and wherein said first and second frequency sensitive potential detecting means respond to, and reject, respectively, signals of said predetermined frequency; whereby any potential to which said potential detecting means responds, may be identified as including, or not including, said predetermined frequency.
Claim 2
Dependent Claim
237 words
A circuit for monitoring a chassis relative to a reference potential comprising in combination; a. a reference potential; b. a chassis; c. a first conductor having distributed resistance coupling said reference potential and said chassis for conducting current in response to a potential difference between said chassis and said reference potential; d. a series circuit comprising a second conductor having a distributed resistance comparable to that of said first conductor and an impedance having a resistance at least a few times greater than that of said distributed resistance and with said series circuit in parallel with said first conductor for conducting current in response to a potential difference between said chassis and said reference potential; e. first and second frequency sensitive potential detecting means in parallel with said impedance for monitoring the potential across said impedance, said last named potential being a function of the potential between said chassis and said reference potential; and f. a power source in parallel with said impedance and having a predetermined frequency, which differs from that of any power supply coupled to any apparatus contained within said chassis, for providing current to said first conductor and said series circuit, and wherein said first and second frequency sensitive potential detecting means respond to, and reject, respectively, signals of said predetermined frequency; whereby any potential to which said potential detecting means responds, may be identified as including, or not including, said predetermined frequency.